One known apparatus for measuring the position of an object comprises a light beam generator for sending a beam of light along an emission axis, and a photoelectric receiver provided with an optical reception system providing a reception field which surrounds a reception axis. The emission axis intersects the reception axis at a fairly short distance from the apparatus to define a volume of space common to both the light beam and the reception field.
When an object moves away from the apparatus in such a manner that it passes through the common volume, the receiver delivers an electrical signal that begins by rising, that passes through a peak as the object passes through the point of intersection of both axes, and that then falls off. The point of intersection is at a defined distance from the apparatus. When the electrical signal passes through its maximum, the object is thus located as being at said point of intersection.
The above apparatus has its drawbacks. It cannot give an immediate reading of the distance to the object. To measure the distance it must proceed with optical scanning of the likely volume (eg. by moving the apparatus itself), until the desired maximum is obtained. This causes the apparatus to be fairly complicated.
Preferred embodiments of the present invention mitigate this drawback.